Due to velocity and position errors, an in-flight vehicle may not be on the desired flight path relative to a target when its sensor first acquires the target. For instance, when the vehicle's sensor acquires the target, the target may not be in the predicted position. The vehicle must then determine the trajectory of the target and must determine the correct intercept flight path. Accordingly, a maneuver is typically required to guide the vehicle from its initial flight path at target acquisition to the flight path required by the vehicle's terminal guidance law. Generally, a large initial course correction is required regardless of the choice of vehicle or guidance law.
Depending on the application, several techniques currently exist for in-flight adjustment of a vehicle's flight path. For example, if the vehicle is within the earth's atmosphere, various control surfaces can be used to turn the vehicle. However, if the vehicle must travel beyond the earth's atmosphere, the vehicle must be equipped with divert motors. If the vehicle is equipped with liquid fuel divert motors, flight path changes can be affected by properly setting the velocity impulses of the divert motor. However, if the vehicle is equipped with solid fuel divert motors, the fixed magnitude burns achieved by the solid fuel motors must be properly scheduled and directed to make the large initial course corrections that place the vehicle on the desired flight path. In either case, it is desirable to minimize the number of divert motors and maneuvers necessary to achieve the desired flight path in order to simplify vehicle design.